Usually IC's are mounted on printed circuit boards and gains contact with in and output signals and further electric components through the circuits on the circuit board. The circuit board is space-consuming, and further the processes used to connect the IC to the circuits on the board requires multiple steps which all must be free of errors. Safe methods have been developed like the mentioned direct connection through a BGA, but long process times are still required. Further the voluminous printed circuit board is a major problem especially in hearing aids and similar electronic devices. In U.S. Pat. No. 5,563,084 a method of making a three dimensionally integrated circuit is disclosed. First and second substrates are provided with devices in at least one layer in at least one surface each. An auxiliary substrate is connected to the one surface of the substrates, which is then reduced in thickness from its opposite surface. The auxiliary layer with the devices thereon is then separated into individual chips, which after having been found to be functioning are aligned and mounted in a side-by-side arrangement on the one surface of the first substrate. Electrical connections are formed between the devices of the mounted chips and the devices in the first substrate. The document does not disclose any way of protecting the individual dice in a wafer level process.
U.S. Pat. No. 6,235,141 discloses a mass production method for integrated optical subsystems. The invention concerns the alignement of singular dies with the dies in a wafer and subsequent bonding of the singular dies with the wafer. Following this the dies are diced to form a bonded pair of dies containing at least one optical element. The document does not disclose any way of protecting the individual dice in a wafer level process.
U.S. Pat. No. 6,177,295 discloses a method for forming individual semiconductor devices by sandwiching a wafer with semiconductor elements on a first side thereon between two glass plates. The devices are diced by sawing.
The object of the invention is to provide a method of producing a signal processing unit comprising an IC, which is faster and less prone to errors, and which is ready for use without the need of an underlying circuit board. In the following the signal processing unit is referred to as an amplifier, but any type of signal processing may take place in the unit.